Reversing a vehicle while towing a trailer can be challenging for many drivers, particularly for drivers that drive with a trailer on an infrequent basis or with various types of trailers. Systems used to assist a driver with backing a trailer frequently estimate the position of the trailer relative to the vehicle with a sensor or the like that determines a steering input for the vehicle based on an input trailer curvature path and determined a hitch angle. Both the hitch angle determination and the steering input determination require use of a kinematic model of the combined trailer and vehicle that includes the length of the trailer, more particularly, from the point of attachment with the vehicle to center of the axles thereof. While some systems have relied on user input for the trailer length, doing so may place an undesired burden on the user and may introduce inaccuracies that some such systems are unequipped to handle. The accuracy and reliability of the calculations involving trailer length can be critical to the operation of the backup assist system. Accordingly, improvements related to automated system estimation of trailer length in an accurate manner may be desired.